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### Delta U equals zero

Posted: Wed Feb 05, 2020 11:58 pm
What would be an example of delta U equaling to zero?

### Re: Delta U equals zero

Posted: Thu Feb 06, 2020 12:03 am
An isothermal expansion

One of the characteristics of an ideal gas is that there is no interaction between gas molecules. This means the molecules will not have any potential energy so the only contributor to the change in internal energy would be its kinetic energy due to its absolute temperature. Since it is isothermal, T=0 so neither kinetic nor potential energy would contribute to the change in internal energy so deltaU=0.

### Re: Delta U equals zero

Posted: Thu Feb 06, 2020 1:14 am
So this is for constant pressure and ideal gas?

### Re: Delta U equals zero

Posted: Thu Feb 06, 2020 1:36 am
it would be for an isothermal reaction when the temperature is constant

### Re: Delta U equals zero

Posted: Thu Feb 06, 2020 1:03 pm
Sorry yes I meant temperature, thanks!

### Re: Delta U equals zero

Posted: Thu Feb 06, 2020 8:03 pm
Considering the first law equation, work and heat would have to equal 0. For an isothermal process, heat is 0, so if there is a reaction that is isothermal that does no work, delta U should be 0.

### Re: Delta U equals zero

Posted: Thu Feb 06, 2020 10:07 pm
delta U would be 0 if it is isothermal and no work is done. imagine a gas expanding in a vacuum with constant temperature. since it is not pushing against anything, no work is done and there is no change in temperature so delta U is 0.

### Re: Delta U equals zero

Posted: Fri Feb 07, 2020 11:08 am
As noted previously, all isothermal processes by definition have delta U = 0. This means that the work done does not necessarily have to be 0. In the case that work is not zero, q will simply be the negative of that so they cancel out.